1. Field of the Invention
The present invention relates to printing paper which is suitable for use in color printing using water-based inks, in particular, color printing using an ink-jet system, and has a feeling and handleability as plain paper, and a printing process using such printing paper.
2. Related Background Art
Ink-jet printing systems have attracted attention because of ready attainment of high-speed, full-color and high-density printing. Printing apparatus making good use of an ink-jet printing system have also spread.
Such exclusive coated paper sheets as disclosed in, for example, Japanese Patent Application Laid-Open Nos. 59-35977 and 1-135682 have been used in such ink-jet printing systems.
With the application of the ink-jet printing systems to a wide variety of fields, paper for ink-jet printing is also required to have higher properties. More specifically, it is required to have, for example, the following properties:
(1) having high ink absorbency and hence being able to quickly dry and fix inks;
(2) causing no so-called bleeding in which when ink dots adjoin, the ink dots run out into each other to unevenly mix with each other;
(3) causing no so-called beading in which a coloring material such as a dye aggregates in the form of a bead on the printing paper to cause unevenness of color strength;
(4) causing no diffusion of ink droplets applied to the printing paper so as to prevent the diameter of an ink dot from growing larger;
(5) providing dots high in optical density and causing no blurring at peripheries of characters and. images;
(6) being excellent in-the coloring property development of a coloring material component in an ink;
(7) having good color reproducibility and providing high-definition images; and
(8) having excellent water fastness.
Meanwhile, a variety of printing apparatus different in printing system exists in the fields of monochromatic printing and business color printing, and there is demand for development of printing paper easy to obtain, low in price and widely usable in the various printing systems.
Viewing paper for ink-jet printing from the above-described points of view, printing paper for ink-jet printing of the coated paper type permits the formation of a high-definition and bright image. When such paper is intended to use as plain paper, however, it involves, for example, the following problems:
(1) it lacks a feeling and handleability as plain paper (PPC paper, general woodfree paper, etc.);
(2) it is poor in writing quality upon writing with a pencil;
(3) it tends to often generate dust due to falling off of components of a coating layer, i.e., often cause dusting;
(4) it lacks flexibility to other printing systems;
(5) it tends to be expensive compared with plain paper; and
(6) it is difficult to form coating layers on both sides of a base paper web, and so printing can be conducted only on one side.
In particular, the occurrence of dusting from the coating layer as described in the problem (3) forms the cause of defective feedability of the printing paper in a printing apparatus. More specifically, a feeding system in a printing apparatus is generally of the type that rubber rollers or the like are brought into contact with the surface of a paper sheet to be fed to feed the sheet by frictional force generated at this time. When dust attaches to the rubber rollers or the like, the desired frictional force can not be obtained, so that the paper sheet tends to undergo defective feedability, which interferes with feeding of the paper sheet into the apparatus, feedability of the paper sheet in the apparatus or discharging of the paper sheet from the apparatus. The problem of such defective feedability particularly markedly arises in the case where a feeding roller comes into contact with the front surface of the paper sheet. Even in the case where the feeding roller comes into contact with the back surface of the paper sheet, however, dust may be often generated due to the contact of the coating layer with parts in the apparatus, such as a guide, and is then suspended in the apparatus to attach to the rubber rollers or the like, thereby causing the same problem as described above.
Meanwhile, printing paper of the plain paper type, which is in commonest use in offices at present, is toner-transfer paper (paper for PPC) for copying machines and the like making use of an electrophotographic system disclosed in Japanese Patent Application Laid-Open Nos. 51-13244, 59-162561 and 59-191068. Among these paper sheets for PPC, there has not been yet found any paper sheet having sufficient ink-jet printability.
The use of the paper for PPC, which is in common use at present, in ink-jet printing may involve, for example, the following disadvantages in many cases.
(1) Absorbency of water-based ink is poor, so that when a great amount of an ink is applied to the paper, the drying and fixing of the ink are delayed (if an object comes into contact with the printed surface in the state that the ink is neither fixed nor dried, the image formed is impaired).
(2) A water-based ink feathers along fibers making up the paper at the time the ink is absorbed in a paper layer, so that the so-called feathering, in which ink dots grow too large, and/or the peripheries of the ink dots become jagged and blurred, occurs, resulting in a failure of the provision of clear characters and images.
(3) In printing of color images, the so-called bleeding, in which when ink dots of different colors are printed adjoiningly to each other, the ink dots run out into each other to cause undesired color mixing, occurs, so that the clearness and coloring of the image formed are impaired, resulting in a failure of the provision of satisfactory images in many cases. For example, when bleeding occurs at boundaries between solid printed areas of different colors, clarity of the boundaries may be impaired, the colors may bleed, or uneven color mixing may be observed.
(4) The water fastness of the image formed is insufficient because the paper for PPC has no special construction for fixing water-soluble coloring materials such as dyes.
(5) The coloring material such as a dye used in an ink penetrates into the interior of the paper together with a solvent for the ink, so that the coloring property of the coloring matter becomes insufficient.
It is an object of the present invention to provide printing paper having a feeling and handleability as plain paper while retaining excellent printability of special exclusive paper for ink-jet for water-based inks.
Another object of the present invention is to provide printing paper both sides of which can be used as printing surfaces, and which is also suitable for use in ink-jet printing.
A further object of the present invention is to provide printing paper suitable for use in ink-jet printing and hard to cause a feeding trouble even in a printing apparatus using any of feeding systems.
A still further object of the present invention is to provide an ink-jet printing process using these printing paper sheets.
Such objects can be achieved by the present invention described below.
According to the present invention, there is thus provided printing paper comprising, as principal components, pulp fibers and a filler, wherein fine particles having a particle diameter within a range of from 5 to 200 nm are held on the pulp fibers exposed on at least one surface of the printing paper in a state that their fibrous form is retained.
According to the present invention, there is also provided an ink-jet printing process comprising the step of applying droplets of an ink to the printing paper described above to conduct printing.
According to the present invention, there is further provided a printing system comprising an ink-jet printing apparatus and printing paper used therein, wherein the printing paper is the printing paper described above.
According to the present invention, there is still further provided an ink-jet printing process comprising using an ink-jet printing apparatus comprising a feeding means adapted to come into contact with one surface of a printing paper sheet among a stack of printing paper sheets to feed the printing paper sheet to a printing position, and a means for separating the printing paper sheet from the stack of printing paper sheets to conduct printing on the printing paper described above.